The present invention is related to riveting and in particular to forming riveted pivot joints including a desired amount of clearance.
It is common in manufacturing to form a joint in which a rivet serves the dual purposes of both fastening two or more parts together and acting as a pivot shaft, as in pliers joints, scissors joints, wire cutters, or various types of pinions. Rivet tension or clearance in such a joint is a factor in determining the amount of friction between two or more pivotally interconnected members. In a joint in a tool such as pliers, it is usually desired to have two or more members in pivotal contact with one another, but not held so tightly together that friction interferes with their use, nor with so much clearance that the parts of a tool feel loose or sloppy with respect to each other. In the case of scissors or wire cutters, looseness may detract from the effectiveness of the tool in its primary cutting function. Such a tool with a loose or sloppy rivet joint is commonly perceived as having low quality.
The most widely used method of controlling the amount of tension or clearance in rivet joints, particularly in tools whose parts pivot with respect to each other, is manual adjustment. That is, after a rivet joint has been formed by machinery, hand tools are used to tighten or loosen the joint as necessary. This often results in inconsistent quality of pivot joints or imperfections in the appearance of a rivet head.
What is needed, therefore, is an improved method and apparatus for automatically forming rivets to form joints having a very small, but accurately established, amount of clearance between the parts riveted together, so that the parts are pivotally movable with respect to one another, with neither excessive friction nor excessive clearance, and without the need for manual adjustment.
The present invention provides a method and apparatus for mechanically forming a rivet in a riveted pivot joint that interconnects a group of parts and reliably provides a desired amount of clearance despite variations in the total thickness of parts being joined.
In accordance with the method of the present invention, a set of parts to be riveted together is clamped together and supported by a parts clamp that moves the set of parts and a rivet held in an aligned set of rivet holes in the parts to a position in which a preformed first head of the rivet is supported by a rivet support anvil. An initial condition or preliminary position of the parts and the rivet with respect to the rivet support anvil is thereby established. Thereafter, a parts support anvil is adjusted with respect to the rivet support anvil to provide the desired amount of clearance in the riveted joint. The opposite end of the rivet is then upset to form a second head, while the rivet support anvil supports the preformed first head of the rivet independently from the parts support anvil.
The method may include a step of moving the parts support anvil a predetermined distance from initial or preliminary position with respect to the rivet support anvil.
In the method of the present invention, establishing the initial condition or preliminary position of the parts support anvil and rivet support anvil with respect to each other, with the parts and rivet being urged against the rivet support anvil, compensates automatically for the actual dimensions of the rivet and the parts being interconnected, and thus compensates for slight manufacturing variations in the parts, in order to provide a joint having the required amount of clearance. It should be understood that the desired or required amount of clearance may be zero clearance, and that during the process of forming a rivet the parts being interconnected may be compressed, where the desired or required clearance is an interference or negative clearance resulting in tension in the rivet when the joint has been completed.
The present invention also provides apparatus for forming a rivet joint according to the method of the invention, the apparatus including a parts support anvil, a parts clamp, a rivet support anvil capable of supporting a first or preformed head of a rivet located in a set of aligned rivet holes through the parts to be riveted together, and a mechanism associated with the parts support anvil, arranged to move the parts support anvil precisely and to hold it in an adjusted position to cause it to support the parts relative to the rivet support anvil so that when a second rivet head is formed on the opposite end of the rivet the rivet joint will have the desired amount of clearance.
Apparatus which is a preferred embodiment of the invention includes a mechanism to hold the parts clamp and parts support anvil in an initial condition, and a mechanism for adjusting the relationship between the rivet support anvil and the parts support anvil from the initial condition to a condition in which formation of the second head of the rivet provides the required clearance.
In a preferred embodiment of the invention a set of arched leaf springs support the parts support anvil, and its position is adjusted by pressing on the leaf springs to straighten them somewhat and thus elongate them to move the parts support anvil.
In one preferred embodiment of the invention a hydraulic piston and cylinder assembly is used to straighten the leaf springs and to hold them in a required position.
In one preferred embodiment of the invention a sensitive transducer is used to detect and measure movement of the parts support anvil and electrically controlled valves are operated in response to signals produced by the transducer to control movement of the parts support anvil.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.